As devices for realizing a virtual reality (VR) technology in which users are provided with virtual images as if they were real events and an augmented reality (AR) technology in which real images are displayed with various types of information superimposed thereon, head-mounted display (HMO) devices have been recently developed.
The display screen of an HMD device is placed in front of the eyes of a user when he or she is wearing the device, and there are see-through HMO devices through which outside states can be seen over the display screen, and non-see-through HMD devices whose display screen blocks the field of view of users. While outside states can be easily observed through a see-through HMD device, it is difficult to obtain a sense of immersion in display of the display screen with such devices since users are affected by light and the like of the outside environment. On the other hand, since outside visual information is blocked from users by non-see-through HMD devices, it is said that the non-see-through HMO devices are better when users want to concentrate on listening to and viewing content, working, and the like. For example, Patent Literature 1 discloses a technology relating to a non-see-through HMO device which can display more satisfactory images by preventing contaminants such as dirt or dust from entering a lens barrel in which a display screen is installed.